High hardness, wear resistant materials

ABSTRACT

A powdered admixture of a boron, carbon, nitrogen or silicon derivative of a first metal, e.g., tungsten carbide, and a source of a second metal, e.g., molybdenum subcarbide when the second metal is molybdenum, is, when subjected to densification conditions, partially reacted and converted to a hard, wear resistant material. Such a material, formed from an admixture of tungsten carbide and molybdenum subcarbide, contains tungsten monocarbide and at least one mixed tungsten/molybdenum carbide. This material has a Vickers hardness of at least about 2200 kg/mm 2  measured using a 1 kg load. Articles formed from this material can be useful as, for example, nozzles in abrasive or nonabrasive waterjet cutting machines and various parts of wire drawing apparatus.

Cross-Reference to Related Application

This application is a Continuation-In-Part of application Ser. No.247,054 filed Sept. 20, 1988.

Background of the Invention

This invention generally concerns a product prepared from an incompletereaction of a mixture of a boron, carbon, nitrogen or silicon derivativeof a first metal, a source of a second metal and, optionally, boron,carbon, nitrogen or silicon. This invention particularly concerns amaterial prepared from a product of an incomplete reaction betweentungsten carbide (WC) as the derivative of the first metal andmolybdenum subcarbide (Mo₂ C) as the source of the second metal. Thisinvention further concerns wear resistant articles formed from suchmaterials.

Tungsten carbide cemented with cobalt is a material of widely knownutility for use in cutting tools and in other applications requiringhigh hardness. For example, tungsten carbide/cobalt is used in abrasivewaterjet cutting nozzles. Unfortunately, cobalt is a strategic material.As such, its price and availability can be subject to political factors.These considerations, among others, provide a basis for many longstanding programs aimed at finding replacements for tungstencarbide/cobalt.

It would be desirable to have one or more nonstrategic materials whichwould provide improvements in terms of hardness over tungstencarbide/cobalt, but at a lower cost than diamond. It would also bedesirable to have a process which allowed production of complex, nearnet shapes which cannot be made by casting molten carbides or by hotpressing.

Summary of the Invention

In one aspect, the present invention is a material suitable for use infabricating articles of manufacture requiring high degrees of hardnessor wear resistance, the material comprising at least one product of anincomplete reaction between AX, a source of B, and, optionally, anamount of X, said reaction product comprising at least one compound AXand at least one compound ABX, wherein A and B are different materialsselected from the group consisting of titanium, zirconium, hafnium,vanadium, niobium, tantalum, chromium, molybdenum and tungsten and X isselected from the group consisting of boron, carbon, silicon andnitrogen. The reaction product may also comprise a residual amount ofthe source of B if such is not completely consumed in forming thecompound(s) ABX. The reaction product, when sufficiently densified,provides the desired hardness and wear resistance.

In a related aspect, the present invention is a method of preparing amaterial suitable for use in fabricating articles of manufacturerequiring high degrees of hardness or wear resistance, the methodcomprising subjecting a powdered admixture of AX and a source of B, and,optionally, an amount of X, AX and the source of B each having a meltingpoint, to conditions of temperature and pressure sufficient to produce asubstantially fully dense, consolidated product of an incompletereaction between AX, the source of B and, optionally, X, said producthaving minimal grain growth and comprising at least one compound AX andat least one compound ABX, wherein A and B are different materialsselected from the group consisting of titanium, zirconium, hafnium,vanadium, niobium, tantalum, chromium, molybdenum and tungsten and X isselected from the group consisting of boron, carbon, silicon andnitrogen, the temperature being less than about three fourths of thelesser of the melting points of AX and the source of B. It is believedthat temperatures in excess of three fourths of the lesser melting pointlead to excessive grain growth and drive the reaction toward completereaction of the AX. These results are believed to be undesirable. Theconsolidated product suitably has a Vickers hardness of at least about1900 kg/mm² measured using a 1 kg load. The Vickers hardness isbeneficially at least about 2200 kg/mm². The process may furthercomprise one or more preliminary steps such as forming the powderedadmixture of AX and a source of B, and converting the admixture into ashaped greenware article. The process may also comprise one or morefinishing steps subsequent to densification.

In another related aspect, the present invention is an improvedwear-resistant article formed from materials prepared by the foregoingprocess. Although SiC and B₄ C have greater hardness than materials ofthe present invention wherein AX is tungsten carbide and the source of Bis Mo₂ C (See Table II), the latter materials have surprisingly improvedwear resistance and performance in extreme wear applications such asnozzles, e.g., waterjet cutting nozzles or mixing tubes, abrasive blastnozzles, water blast nozzles, spray dry nozzles, paint spray nozzles andthe like. The materials of the present invention are also useful inother applications such as orifices, e.g., choke valves and flow meterparts; bushings; pump and valve parts; tiles, sleeves, chutes, tubes andother parts used in handling abrasive materials such as coal or mineralslurries: cutting tools, e.g., indexable inserts, end mills, routerbits, reamers, drills, saw blades, and knives used, where appropriate,for machining or cutting materials such as metals, plastics, woodproducts and composites; dies, capstans, rollers, guides, punches,forming tools and the like used for wire drawing, tube drawing,extrusion, molding, textile manufacturing and other operations requiringhardness or wear resistance; powder compacting dies; EDM currentcontacts and guides: sporting equipment: and precision parts fortimepieces, computers, guns, gyroscopes and the like. This listing ofsuitable applications is solely for purposes of illustration and is notintended to be a definitive listing of all potential applications. Otheruses should be readily apparent without undue experimentation.

Brief Description of the Drawing

FIG. 1 is a graphic portrayal of Vickers Hot Hardness Test data forExample 1 and Comparative Examples A and F in contrast to literaturevalues reported for an alloy of Al₂ O₃ and TiC.

FIG. 2 is a graphic portrayal of the relationship between VickersHardness and wear resistance for the densified materials of Examples 1and 8-13 wherein A is tungsten, B is molybdenum and X is carbon. Thestarting Mo₂ C content, based upon weight of starting powder, for eachof the points is as follows: A=50 wt-%; B=20 wt-%; C=12 wt-%; D=6 wt-%;and E=1 wt-%.

FIG. 3 is a graphic portrayal of the relationship between VickersHardness and starting Mo₂ C content for the densified materials ofExamples 9-13 and Comparative Examples K-N.

FIG. 4 is a graphic portrayal of the hot isostatic press cycle ofExample 21 in terms of time versus pressure.

Detailed Description of the Invention

The present invention employs a material AX wherein A is selected fromthe group consisting of titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum and tungsten and X is selected from thegroup consisting of boron, carbon, silicon and nitrogen. A isbeneficially tungsten, hafnium or titanium, desirably tungsten ortitanium and preferably tungsten. X is beneficially carbon, silicon ornitrogen, desirably carbon. As such, tungsten carbide is a preferred,commercially available material. The tungsten carbide has an averagegrain size which is suitably about ten microns or less, beneficiallyabout five microns or less, desirably about one micron or less andpreferably from about 0.4 to about 0.8 microns. Acceptable gain sizesfor other materials of the formula AX approximate those for tungstencarbide and are readily determined without undue experimentation. Thematerial AX is preferably in powder or particulate form.

Addition of one or more auxiliary or binding metals, such as those ofthe iron group, e.g., cobalt, while permissible provided they do notadversely affect physical properties of resultant compositions, isbelieved to be unnecessary. Although cobalt is not an essentialcomponent, inadvertent addition of trace amounts is believed to beunavoidable if milling or attritor media used to form powdered mixturescontain an amount of cobalt. Cobalt, in particular, aids in formingmixed carbides which may lower densification temperatures to about 1400°C. or lower, depending upon the composition. However, cobalt is notbelieved to be essential for complete densification. One need only usehigher temperatures in the absence of cobalt to approach or achievecomplete densification.

The present invention also employs a source of B. B is selected from thegroup consisting of titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum and tungsten. B is also not the same asA. In other words, when A is tungsten, B may be any of theaforementioned materials other than tungsten B is beneficiallymolybdenum, vanadium, zirconium, chromium, and, when A is not tungsten,tungsten. B is desirably molybdenum or chromium, and preferablymolybdenum. The source of B is preferably in powder or particulate form.

The source of B includes the aforementioned metals as well as the boron,carbon, silicon and nitrogen derivatives thereof. The derivative, whereused, is desirably chemically consistent with AX. That is, if X iscarbon, the derivative of B is desirably a carbide or subcarbide if B.By way of illustration, sources of molybdenum include molybdenum metal,molybdenum carbide (MoC), and molybdenum subcarbide (Mo₂ C). If B is anelemental powder, such as molybdenum metal, one may, if so desired, addan amount of X, carbon in this instance, which is desirably less than orequal to that amount needed to equate stoichiometrically with othersources of molybdenum such as MoC and Mo₂ C. Addition of more than astoichiometric equivalent, while possible, may leave residual unreactedX, carbon in this instance, which, in turn, may adversely affectphysical properties e.g., Vickers Hardness, of resultant densifiedmaterials.

A preferred source of molybdenum is the subcarbide Mo₂ C. Mo₂ C isbelieved to serve as a source of both molybdenum and carbon forpreparation of the mixed carbides. A suitable, but less preferred,source of molybdenum is molybdenum metal. Another suitable, but evenless preferred, source of molybdenum is molybdenum carbide (MoC).Combinations of two or more sources of molybdenum also providesatisfactory results. The molybdenum source is preferably in powder orparticulate form.

The source of B is beneficially employed in an amount sufficient toallow the formation of at least one compound ABX wherein A, B and X areas defined herein. The amount is desirably sufficient to form saidcompound(s) without providing such a large residuum that physicalproperties or performance of the reaction product is degraded enough tocause the reaction product to have no practical utility. The amount isalso desirably less than that which would fully react all of AX. Suchamounts vary depending upon the source of B, but are readily determinedwithout undue experimentation.

By way of illustration, the source of B, when B is molybdenum, isbeneficially employed in an amount sufficient to allow the formation ofat least one tungsten-molybdenum mixed carbide The molybdenum source isdesirably employed in an amount sufficient to provide the finalcomposition with a molybdenum content of about one weight percent ormore. When the molybdenum source is Mo₂ C, the amount is suitably fromabout one to about thirty, desirably from about three to about 20, andpreferably from about six to about ten, percent by weight, based uponthe weight of the total amount of Mo₂ C and WC starting materials.

The process of the present invention suitably comprises subjecting apowdered admixture of AX, a source of B, and, optionally, X todensification conditions sufficient to produce a consolidated product ofan incomplete reaction between AX and B, said product comprising atleast one compound AX and at least one compound ABX. The variables A, Band X are as defined herein. The densification conditions are selectedto minimize grain growth and include a temperature which is less thanabout three fourths of the lesser of the melting points of AX and thesource of B, but greater than a temperature at which no appreciableconsolidation occurs, and a pressure sufficient to achieve a desirabledegree of densification. The reaction product is preferablysubstantially fully dense.

As used herein, the terms "incomplete reaction", "incomplete reactionproduct" and "product(s) of an incomplete reaction" all refer to thereaction between AX and the source of B wherein at least a portion of AXdoes not react with the source of B. As a consequence, that portion isadmixed with ABX and, optionally, a small amount of the source of B inproducts prepared in accordance with the present invention.

When A is tungsten, B is molybdenum and X is carbon, the densificationconditions are beneficially sufficient to produce a material having aVickers hardness, measured using a 1 kg load, of at least about 2200kg/mm². The Vickers hardness is desirably more than about 2300 kg/mm²and preferably more than about 2400 kg/mm². Lower Vickers hardnessvalues, e.g., about 1900 kg/mm² or less, are readily attainable if thematerial is to be used in applications wherein the higher hardnessvalues are not needed. One means of attaining such lower values is toselect molybdenum metal as the molybdenum source.

When elements other than tungsten, molybdenum and carbon aresubstituted, respectively, for A, B and X, the resultant densifiedmaterials can provide Vickers hardness values as low as about 1000kg/mm². FIG. 2 shows a generally linear relationship between Vickershardness and wear resistance for the tungsten/molybdenum/carbondensified materials. Analogous densified materials, obtained from theaforementioned substitutions, should behave similarly. As such, the wearresistance of a 1000 kg/mm² Vickers hardness material should be muchlower than that of a 2400 kg/mm² Vickers hardness material. Because ofchemical compatibility or other reasons, the lower hardness materialsmay, however, still show exceptional utility in certain applications.

The powdered admixture may be prepared by any one of a number ofconventional mixing processes so long as a generally uniform admixtureis obtained and no adverse effects upon physical properties of theresultant material are observed. The use of an attritor, wherein ballsof hard material are used to facilitate mixing, provides particularlysatisfactory results even if small portions of the balls, typicallyformed from a tungsten carbide/cobalt material, are abraded therefromduring mixing and added to the admixture. The presence of a minor amountof cobalt in reaction products or final materials does not adverselyaffect the physical properties of the densified material. The use ofballs formed from the same material as that being mixed, e.g., tungstencarbide/molybdenum carbide balls where A is tungsten, B is molybdenumand X is carbon, reduce the inadvertent addition of cobalt.

The starting materials, AX, the source of B, and, optionally an amountof X, are beneficially in particulate or powder form before they areconverted to an admixture. When AX is tungsten carbide and B ismolybdenum, the starting materials suitably have an average particlesize of less than about 5 microns. Mo₂ C powders, the preferred sourcematerial when B is molybdenum, are commercially available in at leasttwo average particle sizes: four microns and two microns. It is believedthat small particles, particularly of Mo₂ C, offer more advantages thanlarge particles, at least in terms of hardness, wear and residualunreacted Mo₂ C. Small particles, as a general rule, also require lessmixing time than large particles. As such, the powders desirably have anaverage particle size of less than about 2 microns. Similar particlesizes suffice for other starting materials of the present invention

Mixing of the powders in an attritor is beneficially accomplished withthe aid of a liquid such as heptane. In order to facilitate greenwareformation subsequent to mixing, a binder such as paraffin wax can beadded during the final stages of attrition. Desirably, the attritedmixture is dried before further processing. Particularly satisfactoryresults are obtained by screening or classifying the attrited and driedmixture to remove unwanted agglomerates and fines.

The process of the present invention may also comprise a secondpreliminary step wherein the attrited, dried and classified mixture isconverted to a preform. Preforms can be prepared using technology knownin the powder metals or ceramics industries. See. e.g., U.S. Pat. No.4,446,100; and Modern Ceramic Engineering, Chapter 6, pages 178-215(1982), the teachings of which are incorporated herein by reference.

A typical procedure for converting a particulate material, which cancontain reinforcements, fillers, densification aids, binders,lubricants, dispersants, flocculants, etc., into a preform begins byforming or shaping the powder into a desired configuration usinguniaxial pressing, isostatic pressing, slip casting, extrusion,injection molding or any similar technology. The resulting article isthen prepared for densification by thermal or chemical debindering,pre-sintering, green machining, reisopressing, and the like. Aprotective coating can be applied to the resulting article to preventreaction with the environment. In extreme cases, the article can be"canned", or placed in an impervious container, to permit handlingwithout atmospheric contamination. The resulting article, as preparedfor densification, is referred to herein as "greenware".

When B is molybdenum, densification is suitably conducted at atemperature of less than about 1600° C. Temperatures in excess of 1600°C., e.g., about 1650° C., offer no appreciable advantages in terms of anincrease in density. Such temperatures do, however, provide asignificant disadvantage in that they promote grain growth which isbelieved to adversely affect performance of the densified material inpractical considerations like hardness. Temperatures which are too lowto achieve adequate densification are unacceptable. It is believed thatadequate densification cannot be achieved much below about one-half themelting temperature of the molybdenum source. Of the three preferredmolybdenum sources, molybdenum metal, Mo₂ C and MoC, molybdenum metalhas the lowest melting point at 2617° C. As such, a reasonable lowertemperature limit for densification is about 1300° C. The range oftemperatures for densification is desirably from about 1350° C. to about1500° C. Temperature ranges for other combinations of AX and B arereadily determined without undue experimentation.

The greenware is subjected to pressure assisted densification using oneof several techniques known to those skilled in the art whereby thegreenware is desirably subjected to pressure at elevated temperatures toproduce a desired article. These techniques include hot pressing, hotisostatic pressing (HIP'ing) and rapid omnidirectional compaction (ROC).Although any of these techniques may be used with varying degrees ofsuccess, particularly suitable results are obtained by the ROC techniquewhich employs mechanically induced pressure, e.g., that generated byusing a forging press, as a means of densifying greenware.

A desirable method of converting the greenware into a satisfactorydensified article is described in U.S. Pat. No. 4,744,943, the teachingsof which are incorporated herein by reference. When such a method isemployed, the pressure is suitably applied for a period of time of lessthan about one hour. The period of time is beneficially less than aboutthirty minutes, desirably less than about one minute and preferably lessthan about ten seconds. In order to facilitate recovery of resultantdensified parts, the greenware is beneficially wrapped in graphite foilor some other substantially inert material prior to being placed in aglass pocket fluid die or other densification medium.

U.S. Pat. No. 4,081,272 discloses a glass-encapsulated HIP process. U.S.Pat. No. 3,622,313 discloses a HIP process. The teachings of thesepatents are incorporated herein by reference. If the glass-encapsulatedprocess is used, a desirable modification includes evacuating the glasscapsule containing a part to be densified and eliminating the use ofpowdered glass. Application of pressure suitably occurs over a period ofone hour or less.

The densified article prepared in the manner described hereinabove is acomplex, multi-phase, fine-grained composite containing, as principalcomponents, at least one compound ABX and at least one compound AX. WhenA is tungsten, B is molybdenum and X is carbon, the reaction productwill contain tungsten carbide and at least one mixed carbide of tungstenand molybdenum (W, Mo)C. The mixed carbide will have varyingstoichiometry and an average composition comprising from about 60 toabout 99 percent by weight tungsten, from about one to about 40 percentby weight molybdenum and from about four to about nine percent by weightcarbon. The average composition is desirably from about 77 to about 89percent by weight tungsten, from about 5 to about 16 percent by weightmolybdenum and from about 5 to about 8 percent by weight carbon. If thesource of B is not fully converted to the compound ABX, the reactionproduct will also contain an amount of said source of B, e.g., Mo₂ C.The amount may vary from as little as a trace amount, e.g., about 0.01percent by weight or less, to a much larger quantity depending upon avariety of interrelated variables. Such variables include startingmaterial selection, adequacy of mixing, and densification parameters.Finally, if an attritor is used for mixing and the balls containedtherein are formed at least partially from a material other than thestarting materials, e.g., cobalt, that material may be incorporated intothe composite as, for example, part of an additional mixed carbidephase.

The densified article exhibits surprisingly improved hardness and wearresistance in comparison to a like article formed from tungstencarbide/cobalt. The Vickers hardness of an article representative of thepresent invention, e.g., that produced when A is tungsten, B ismolybdenum and X is carbon, is suitably at least about 2200 kg/mm²measured using a 1 kg load. The Vickers hardness is beneficially atleast about 2300 kg/mm², and desirably at least about 2400 kg/mm². Asnoted hereinabove, lower Vickers hardness values on the order of 1900kg/mm² or even lower may be acceptable for some applications. Also asnoted hereinabove, those hardness values are readily attainable with theprocess of the present invention. The article suitably exhibits anabrasion wear resistance of at least about 500 cm⁻³ measured by the ASTMG65-80 method. The abrasion wear resistance is desirably at least about550 cm⁻³. The article beneficially exhibits an erosion wear rate of nomore than about 3×10⁻³ mm³ /g of abrasive measured at a 30 degree anglemeasured by the ASTM G76-83 method. The article desirably exhibits anerosion wear rate of no more than about 2×10-3 mm³ /g of abrasivemeasured at a 90 degree angle measured by the ASTM G76-83 method.Although lower wear rates would clearly be desirable, measurement ofsuch rates with currently available equipment is quite difficult, if notimpossible. Skilled artisans will recognize that hardness and wearresistance vary depending upon the materials represented by A, B and X.Skilled artisans will recognize that wear resistance is proportional tohardness and that softer materials may provide an abrasion wearresistance below 500 cm⁻³. These materials may be suitable in extremetemperatures or in chemically aggressive environments.

The densified article suitably has a fine-grained structure with anaverage grain size of less than about ten microns. The grain size isbeneficially less than about five microns and desirably less than aboutone micron.

The articles of this invention generally have a density of about 85percent of theoretical density or greater. The density is beneficiallymore than about 90 percent, desirably more than about 95 percent andpreferably about 100 percent of theoretical density. "Theoreticaldensity", as used herein, is a calculated value based upon volumefraction and density of the starting components. "High density", as usedherein, refers to a density of at least about 90 percent of theoreticaldensity. The material of the invention is particularly useful for thefabrication of cutting tools and nozzles, such as waterjet cuttingnozzles.

Specific Embodiments of the Invention

The following examples and comparative experiments illustrate thepresent invention and should not be construed, by implication orotherwise, as limiting its scope. All parts and percentages are byweight and all temperatures are in ° centigrade (°C.) unless otherwiseindicated. Examples of the present invention are designated by Arabicnumerals whereas comparative examples are identified by capital letters.

Example 1--Preparation of Densified Material using Mo₂ C as theMolybdenum Source

The starting powder is a mixture of 94 percent tungsten carbide powderhaving an average particle size of 0.8 micron, and 6 percent Mo₂ Chaving an average particle size of about four microns. The powdermixture is intensely mixed, in the presence of heptane, in an attritorcontaining fifty kilograms of tungsten carbide-cobalt balls for 8 hours.About 2-3 percent paraffin wax is added as a binder during the lastthirty minutes of attritor mixing. The resultant mixture is dried andscreened through a 20 mesh screen. Greenware parts are made bycold-pressing the mixture which passes through the screen in steeltooling at 5,000 pounds per square inch (psi) (35 MPa). The cold-pressedparts are then cold isostatically pressed at 30,000 psi (210 MPa). Theresultant parts are dewaxed under vacuum at 350° C. The greenware isthen placed into a glass pocket fluid die, or isostatic die assembly,preheated at 1400° C.for 2 hours in a nitrogen atmosphere, and thenisostatically pressed at 120,000 psi (830 MPa) for 5 seconds. Thepressing procedure is described in more detail in U.S. Pat. Nos.4,744,943; 4,428,906; and 4,656,002, the teachings of which areincorporated herein by reference. The fluid die is cooled in air and theparts are recovered and sand blasted.

Analytical work involves the use of metallography, light microscopy,analytical scanning electron microscopy (ASEM), electron probe analysis(EPA), analytical transmission electron microscopy (ATEM), and x-raydiffraction (XRD). Microstructures are observed under the SEM, ATEM, andlight microscopes. Determination of the presence of a reaction phasemakes use of XRD. Composition of the reaction phase is determined by EPAand ATEM. Volume fraction of phases is determined by stereology of BSEimages, and grain counting in ATEM.

Analysis of the composite indicates a bulk composition of 88.3 percentby weight W, 5.6 percent Mo, and 6.1 percent C. The material is adiscrete, multiphase composite including about 28.5 percent by volumeWC, about 70 percent by volume of a mixed tungsten-molybdenum carbide(MoC-WC containing 3-32 mole percent MoC and 0.2 weight percent Co),about 1.3 percent by volume of a mixed cobalt-tungsten-molybdenumcarbide having a cobalt content of 2-10 weight percent, about 0.01percent by volume Mo₂ C, and about 0.2 percent by volume voids. Thematerial is fully granular with no binder phase or continuous phase. Thematerial also displays no discernible grain separation. The mixedtungsten-molybdenum carbide phase is a continuum of compositions in therange of 1.5-19 weight percent Mo, or 3-32 mole percent MoC in the mixedcarbide. The average composition of the mixed carbide phase is 7.2weight percent Mo or 13.7 mole percent MoC in the mixed carbide phase.

Grain size distribution is determined using the intercept methoddescribed by Underwood in Quantitative Stereology, Addison-Wesley,Reading, Mass. (1970). The average grain size is about 0.22 microns,with 80% of the grains having a size of less than 0.3 microns. The finalWC grain size is about 0.25 μm. The physical properties of the parts aresummarized in Table I.

                  TABLE I                                                         ______________________________________                                        Physical Properties of Articles Prepared in Ex. 1                             Property    Measured Value                                                                              Method                                              ______________________________________                                        Density     14.9   g/cm.sup.3 Water                                                                         immersion                                                                     ASTM B311-58                                    Hardness    2650   kg/mm.sup.2                                                                              Vickers-1 kg                                                                  ASTM E384-73                                    Palmqvist   25     kg/mm      Palmqvist                                       Toughness                     indentation                                     (W)                                                                           Strength    950    MPa        Transverse                                                                    rupture                                                                       strength                                                                      ASTM B406-76                                    Wear Rate                                                                     A.    Abrasion 693 1/cm.sup.3   ASTM G65-80                                   B.    Erosion  0.9 × 10.sup.-3 mm.sup.3 /g (30°)                                                 ASTM G76-83                                                  0.7 × 10.sup.-3 mm.sup.3 /g (90°)                 ______________________________________                                    

The data presented in Table I show that the composite exhibitsoutstanding hardness and wear resistance. Similar results are expectedwith other compositions of the present invention.

Example 2--Preparation of Densified Material using Metallic Molybdenumas the Molybdenum Source

The process of Example 1 is repeated except that the Mo₂ C startingpowder is replaced with 11.3 percent Mo. Analytical data indicates thefinal composite is 72 percent WC, 25 percent of a mixed (W, Mo)C phase,and 3 percent Mo₂ C, with the primary binding phase having the followingcompositions: 61 percent W, 33 percent Mo, 6 percent C. The Vickers 1 kghardness of the composite is 1925 kg/mm².

Example 3--Duplication of Example 2 With a Lower Molybdenum MetalContent

The process of Example 2 is repeated except that 6.8 percent Mo isemployed. Analytical data indicates that the final composite has acomposition similar to that of Example 1. The Vickers 1 kg hardness ofthe composite is 2570 kg/mm². Results similar to those shown in Examples1-3 are attainable with other components and process conditions, all ofwhich are disclosed herein.

Comparative Experiments

The tungsten carbide/cobalt material of Comparative Example A is formedinto a greenware part and densified in a manner similar to that ofExample 1. Comparative Examples B-E and G are densified by sintering andComparative Examples F, H and I are densified by hot pressing. Thelatter procedures are well known in the art. The materials ofComparative Examples A-I and the materials produced in Examples 1 and 3are then tested for wear rate as measured by abrasion and erosion. TheASTM G65-80 dry sand rubber wheel test is used to measure abrasion,while erosion is measured according to the procedure of ASTM G76-83.Abrasion wear is recorded as the inverse of the volume loss. Erosiondata is reported as volume loss/gram of abrasive. The results of thesetests, as well as the Vickers hardness for the materials, is reported inTable II.

                  TABLE II                                                        ______________________________________                                               Properties of WC-Mo and WC-Mo.sub.2 C Composities                             Compared to Other Hard Materials                                                           Wear Test Data                                                                          Wear                                            Example/                      Number Erosion                                  Compara-             Vickers  (Abra- (X.sup. -3                               tive                 Hardness sion)   mm.sup.3 /g)                            Example  Material    kg/mm.sup.2                                                                            1/cm.sup.3                                                                           30°                                                                         90°                          ______________________________________                                        3        WC-6.8 Mo   2570     700    2.1  1.0                                 1        WC-6.0 Mo.sub.2 C                                                                         2650     693    0.9  0.7                                 A        WC-6.0 Co   1800     440    21.4 8.7                                          WC/Low Co                                                            B        K-602* (1.5)                                                                              --       275    5.8  4.8                                 C        K-11* (2.8) --       --     4.8  4.3                                 D        K-8* (3.8)  --       --     6.4  3.7                                 E        Al.sub.2 O.sub.3                                                                          2000     --     30.4 39.5                                F        Si.sub.3 N.sub.4                                                                          1550     --     15.0 25.5                                G        SiC         2800     150    --   18.0                                H        B.sub.4 C   3100     139    1.6  1.2                                 I        TiB.sub.2   --       129    --   --                                  ______________________________________                                         *Commercially available from Kennametal Inc. The numbers in parentheses       indicate weight percent of binder material.                                   -- Not measured.                                                         

As can be seen from Table II, the tungsten carbide/molybdenum-containingmaterials of the present invention have surprisingly high hardness andwear-resistance in comparison to tungsten carbide/cobalt and other hardmaterials.

Vickers Hot Hardness Testing

The materials of Example 1 and Comparative Examples A and F aresubjected to Vickers Hot Hardness testing in accordance with theprocedure described by B. North in Engineering Applications of BrittleMaterials, page 159 (1985), the teachings of which are incorporatedherein by reference. Results of the testing, with a one kilogram loadand a ten second indent time at various temperatures, are graphicallydisplayed in the FIGURE. The FIGURE also displays literature valuesreported for an alloy of Al₂ O₃ and TiC. The data shown in the FIGUREindicates the suitability of compositions of the present invention forhigh temperature applications such as cutting tools for metals. Similarresults are obtained with other materials and process conditions, all ofwhich are disclosed herein.

Examples 4-7--Variation of Tungsten Carbide Starting Material Grain Size

The procedure of Example 1 is replicated save for increasing thetungsten carbide starting material average grain size in Examples 5, 6and 7 respectively to 1.6 microns, 3.5 microns and ten microns andincreasing the load for the Vickers Hardness test from one kilogram to13.6 kilograms. Vickers Hardness test results, in kg/mm², are asfollows: Example 4-2480; Example 5-2320; Example 6-2100; and Example7-1925. The Vickers Hardness test data shows that starting materialgrain size affects at least the hardness of the resultant material.Similar results are expected with other materials and processconditions, all of which are disclosed herein.

Example 8 and Comparative Example J--Comparison of Densified MaterialsPrepared by Sintering (Comparative Example J) and by the Process of theInvention

The starting powder for each process is a mixture of 99 percent of thesame tungsten carbide powder as used in Example 1 and one percent of aMo₂ C powder having an average particle size of two microns.

The powder mixture of Comparative Example J is mixed in a ball mill, inthe presence of heptane, for a period of 24 hours. About one percent ofparaffin wax is added during the last thirty minutes of milling.Greenware parts are formed and dewaxed as in Example 1. The parts arethen heated in an argon atmosphere at a temperature of 2225° C. for aperiod of thirty minutes to accomplish densification by sintering. Theparts have a very coarse grain structure, a density of about 96 percentof theoretical density and a Vickers hardness of about 1100 kg/mm².

The powder mixture of Example 8 is converted to densified parts by theprocedure of Example 1. The parts have a very fine grain structure, adensity of about 98 percent of theoretical density and a Vickershardness of about 2750 kg/mm².

A simple comparison of the foregoing results demonstrates that theprocesses provide substantially different results from the same startingmaterials and that the process of the present invention produces a muchharder material. Similar results are obtained with other materials andprocess parameters which are representative of the present invention.

Examples 9-13 and Comparative Examples K-L--Effect of Composition uponResultant Physical Properties

Using varying amounts of the tungsten carbide powder of Example 1 andthe Mo₂ C powder of Example 8, a number of densified parts are preparedby following, with two exceptions, the procedure of Example 1. In oneexception, 100% Mo₂ C powder is processed by the procedure of Example 1except for omission of attritor mixing. In the second exception,greenware parts for Comparative Examples K and L are wrapped in graphitefoil, e.g., that commercially available from Union Carbide under thetrade designation Grafoil®, to facilitate part recovery. The densifiedparts are subjected to the following physical property tests: (a)Vickers Hardness (VHN), with a one kilogram load, in terms of kg/mm² ;(b) Palmqvist Toughness (W), with a 13.6 kilogram load, in terms ofkg/mm; (c) Wear Number (WN), per ASTM G-65-80, in terms of 1/cm³ ; and(d) Volume Losses (VL) at 30° and 90° , per ASTM G-76-83, in terms of10⁻³ mm3/gm. The Palmqvist Toughness test is described by R. Warren andH. Matzke in "Indentation Testing of a Broad Range of CementedCarbides", Science of Hard Materials, pages 563-82, R. K. Viswanadham,D. J. Rowcliffe and J. Gurland eds., Plenum Press (1983). Physicalproperty data obtained from these tests is summarized in Table III whichfollows:

                  TABLE III                                                       ______________________________________                                        Example Physical Property Test Results                                        Compar-                  Wear Test Data                                       ative   %                        VL                                           Example Mo.sub.2 C                                                                             VH      W     WN    30°                                                                          90°                         ______________________________________                                         9      1        2750    24.7  632   0.03  0.10                               10      3        2740    23.9  --    --    --                                 11      6        2650    24.9  600   0.09  0.05                               12      12.6     2540    24.6  564   0.35  0.08                               13      19.8     2350    24.2  521   0.14  0.09                               K       30       2176    21.8  369   0.06  0.02                               L       40       2107    20.8  408   0.11  0.04                               M       50       1690    19.5  299   4.1   2.60                               N       100      1400    --    --    --    --                                 ______________________________________                                         -- not measured                                                          

The data presented in Table III, and graphically portrayed in FIG. 3,demonstrate the suitability of the process of the present invention forpreparing hard, wear-resistant materials from a variety of compositions.Densified materials prepared from starting compositions wherein theamount of Mo₂ C is fifty weight percent or more are clearly softer andless wear resistant than materials wherein the amount of Mo₂ C is twentyweight percent or less. Although not shown in Table III, acceptableperformance may be achieved with an Mo₂ C content of less than thirtyweight percent. Similar results are obtained with other startingmaterials and process parameters, all of which are presented herein.

Example 14--Waterjet Cutting

The procedure of Example 1 is repeated to prepare abrasive waterjetnozzles having a length of two inches and a bore of 0.062 inch. Thenozzle bore is formed by machining the article prepared from theconsolidated or densified powders. The resulting nozzles are testedagainst commercially available tungsten carbide/cobalt nozzles accordingto the following procedure.

The nozzles are installed on a commercially available abrasive jetcutting machine available from Flow Systems, Inc. (Model No. 11x Dual).For a description of an example of a waterjet cutting machine, see U.S.Pat. No. 4,648,215. The water pressure is 35,000 psi and the abrasiveflow rate is 1.5 pounds/minute. The jewel size is 0.018 inch. The nozzlewear rate is determined by measuring the increase in exit bore size as afunction of time. The results are summarized in Table IV.

                  TABLE IV                                                        ______________________________________                                                                   Increase in Exit                                                     Time     Bore Size,                                                                              Wear                                     Composition                                                                             Abrasive                                                                              (Min.)   Inches    Mil/Min.                                 ______________________________________                                        WC/Co     Al.sub.2 O.sub.3                                                                       1       +0.015    15                                       WC/Mo.sub.2 C                                                                           Al.sub.2 O.sub.3                                                                      42       +0.012    0.29                                     WC/Co     Garnet  45       +0.012    0.27                                     WC/Mo.sub.2 C                                                                           Garnet  435      +0.002    0.0023                                   ______________________________________                                    

As can be seen from Table IV, the material of the present inventionwears surprisingly slower than the commercial material using alumina orgarnet as the abrasive. The commercial WC/Co material wears so rapidlywith the alumina abrasive that it is not economically viable in such anapplication. Similar results are expected with other compositions andprocess conditions of the present invention.

In a second series of tests, the procedure is identical except that themachine is a Model 9x Dual, the water pressure is 30,000 psi (208 MPa)and wear rate is measured by the increase in nozzle entrance bore sizeas a function of time. The test is continued until it is observed thatnozzle wear is extensive enough to cause the water/abrasive jet streamto spread and noticeably interfere with the quality of the cut on thework piece or until sufficient time had elapsed to demonstrate theviability of a nozzle. The results are summarized in Table V.

                  TABLE V                                                         ______________________________________                                                          Time    Increase in Entry                                                                         Wear                                    Composition                                                                            Abrasive (Min.)  Bore Size, In.                                                                            Mil/Min.                                ______________________________________                                        WC/Co    Garnet   100     +0.020      0.20                                    WC/Mo.sub.2 C                                                                          Garnet   720     +0.010      0.014                                   ______________________________________                                    

Surprisingly, the test indicates that the material of the presentinvention provides a nozzle which lasts over 14 times longer than thepresent commercially available tungsten carbide/cobalt nozzle. Similarresults are expected with other starting materials and processconditions of the present invention.

Example 15 and Comparative Examples O-P--Effect of Pressure Cycle UponResultant Physical Properties

The process of Example 1 is replicated with the following exceptions:(a) the starting powders and wax are processed in a commercial attritoras is typical for commercial scale production of WC/Co powders; (b)greenware parts are cold-pressed at about 10,000 psi (70 MPa), ratherthan 5,000 psi (35 MPa) as before; (c) the isostatic pressure is variedbetween 15-30 tons per square inch (tsi) (208-415 MPa) maximum pressure(as shown in Table VI); (d) isostatic press dwell time is increased to15 or 30 seconds, also as shown in Table VI; and (e) the greenware iswrapped in graphite foil, commercially available from Union Carbideunder the trade designation Grafoil®, prior to being in placed into theglass pocket fluid die. Recovered parts are subjected to density andhardness measurements as in Example 1. The data obtained from suchmeasurements is presented in Table VI.

                  TABLE VI                                                        ______________________________________                                        Physical Properties of Example 15 and                                         Comparative Examples O-P                                                      Example/  Maximum                                                             Comparative                                                                             Pressure  Dwell   Density VHN                                       Example   (tsi)     (sec)   (g/cm.sup.3)                                                                          (kg/mm.sup.2)                             ______________________________________                                        O         15        10      12.7    1220                                      P         30        10      13.7    1793                                      15        15        30      14.7    2601                                      ______________________________________                                    

A simple comparison of the foregoing results demonstrates that at lowpressures and low dwell times (Comparative Examples O and P), thearticles are clearly of lower density and hardness than those producedin Example 1. However, with low pressure and a longer dwell time(Example 15), a material with properties approximating those of Example1 may be obtained.

Examples 16-20 and Comparative Example Q--Effect of Preheat Temperatureupon Resultant Physical Properties

The process of Example 1 is replicated except for the temperature towhich the parts are preheated just prior to pressure application (thetime of preheat, two hours, is not changed). This temperature is variedfrom 1250° to 1500° C. in 50° C. increments. In addition, the graphitefoil wrap of Example 15 is used for the greenware. Physical propertymeasurements for density and Vickers hardness are made in accordancewith the test descriptions accompanying Example 1. Palmqvist toughness(W) is measured by Palmqvist Indentation. The measurements and preheattemperature are found in Table VIII.

                  TABLE VII                                                       ______________________________________                                        Physical Properties of Example 16-20 and                                      Comparative Example Q                                                         Example/                                                                      Comparative                                                                             Preheat  Density   VHN     W                                        Example   T (°C.)                                                                         (g/cm.sup.3)                                                                            (kg/mm.sup.2)                                                                         (kg/mm)                                  ______________________________________                                        Q         1250     14.6      2446    23.8                                     16        1300     14.9      2612    24.4                                     17        1350     14.9      2545    24.0                                     18        1400     15.0      2726    23.9                                     19        1450     15.0      2675    24.4                                     20        1500     15.0      2551    24.2                                     ______________________________________                                    

By comparison with the data from Example 1, it can be seen that in orderto produce similar material, the preheat temperature is suitably above1300° C. If a material of lower hardness can be tolerated, a lowerpreheat temperature may be used.

Comparative Example R--Consolidation of the Material by Application ofTemperature without Pressure

The process of Example 15 is repeated except that the parts arecold-pressed using a dry bag isopress with 0.609 inch diameter tooling,with 30,000 pounds per square inch (208 MPa) pressure and a dwell timeof 10 seconds. They are then dewaxed and loaded into fluid dies as inExample 1, and preheated at 1400° C. for two hours. The preheated partsare removed from the furnace without application of pressure and allowedto cool. The parts are recovered as in Example 1. ATEM (AnalyticalTransmission Electron Microscopy) shows evidence of some reactionbetween WC and Mo₂ C, but to a much lesser extent than observed inExample 1 wherein the preheated parts are subjected to isostaticpressure of 120,000 psi (830 MPa) for 5 seconds after removal from thefurnace.

Analysis of the parts using the analytical techniques of Example 1indicates a bulk composition of about 62 percent by volume WC, about 28percent by volume of a mixed tungsten-molybdenum carbide similar to thatfound in Example 1 (reaction product I), about 2.5 volume percent of ahigh-Mo mixed tungsten-molybdenum carbide (reaction product II), about1.5 volume percent unreacted Mo₂ C, and about 6 volume percent voids.Reaction product I contains an average of about 6.8 weight percent Mo,with the range extending from about 1.8 to 17.9 weight percent Mo.Reaction product II is MoC/-WC product of varying stoichiometry with anaverage of 48 weight percent Mo, ranging from 27 to 72 weight percentMo.

Comparative Example R contains considerably more unreacted WC than thematerial of Example 1 (62 percent vs. 28.5 percent). In turn, it alsocontains less of the mixed carbide reaction product A, with only 28percent as compared to 70 percent in Example 1. Example R also containsreaction product B, a partially reacted molybdenum carbide, whichExample 1 does not have, and about 1.5 weight percent unreacted Mo₂ Ccompared to 0.01 percent in Example 1. These observations suggest thatpressure is necessary to achieve an acceptable reaction between the twocarbides, at least at a preheat temperature of 1400° C. The currentexample also contains more voids than the first, due to poordensification.

The parts have a much higher porosity than those of Example 1, 6 volumepercent voids versus 0.2 volume percent voids. The high porosityprecludes an accurate density measurement. The Vickers 1 kg hardness is573 kg/mm², considerably lower than the 2650 kg/mm² of Example 1. Thesedifferences indicate that parts prepared without sufficient applicationof pressure are unsuitable for applications requiring high hardness.Because of the relationship between hardness and wear resistance, theseparts are also believed to be unsuitable for applications requiringsubstantial wear resistance.

Example 21--Preparation of Densified Material by Hot Isostatic Pressing

The process of Example 15 is repeated through the step involving coldisostatically pressing of the greenware at 30,000 psi. The resultantparts are dewaxed under vacuum at 350° C. and subsequently presinteredat 1400° C. in order to reduce the possibility of outgassing during hotisostatic pressing (HIP). The greenware is then placed in a Pyrexampule, which is evacuated and sealed. The encapsulated part is placedin a HIP unit, and subjected to a gradual increase in pressure (see FIG.4 for a graphic portrayal of cycle) up to 30,000 psi (208 MPa). Thetemperature is concurrently increased to 1400° C. The pressure of 30,000psi (208 MPa) and the temperature of 1400° C.are maintained for onehour. Pressure and temperature are then gradually decreased and the partremoved upon completion of the cycle. The part, following recovery fromthe ampule, is subjected to physical property testing as in Example 1.The physical properties are as follows: Density-14.8 g/cm³ ; Vickershardness-2598 kg/mm² ; and Palmqvist Toughness (W)-22.5 kg/mm. Theseproperties compare favorably with those of Example 1 and suggest thatHot Isostatic Pressing is a viable alternate procedure to that describedin Example 1.

Example 22--Preparation of Densified Material Incorporating an Amount ofX

The process of Example 15 is replicated except that the starting powdersare changed to provide a mixture of 94 percent WC, 5.6 percent Mo, and0.4 percent carbon black. The resultant densified material has a Vickers1 kg hardness measurement of 2460 kg/mm². This hardness measurementsuggests that substitution of an amount of X for a like amount of thesource of B does not substantially reduce physical properties of theresultant densified material. It also suggests that the densifiedmaterial should be useful for wear resistant applications.

Comparative Example S--Preparation of Densified Material using a Mixtureof Elemental Powders

The process of Example 22 is replicated except that the starting powdersare changed, and a smaller attritor is used (3.5 kg load of WC/Coballs). The starting powders are 88.2 percent W, 5.6 percent Mo, and 6.2percent carbon black. The resultant densified material has a Vickers 1kg hardness measurement of 725 kg/mm². This hardness measurementsuggests that mixtures of elemental powders do not provide satisfactorydensified materials. It also suggests poor wear characteristics. Similarresults are attainable with other mixtures of elemental powders.

Example 23--Preparation of Densified Material using Chromium Carbide asthe Source of B

The process of Example 1 is, with certain exceptions, repeated using achromium carbide rather than Mo₂ C as a source of B. The exceptions are:(a) use of the attritor of Comparative Example S; (b) cold pressing at10,000 psi (70 MPa) rather than 5,000 psi (35 MPa); (c) greenware iswrapped in graphite foil as in Example 15: and (d) a preheat temperatureof 1500° C. rather than 1400° C. The starting powder is a mixture of95.5 percent of the same tungsten carbide powder as in Example 1 and 4.5percent chromium carbide powder having an average particle size of -325mesh (less than about 48 microns).

Analysis of the composite indicates about 3.3 volume percent unreactedCr₃ C₂, about 0.8 volume percent chromium-tungsten carbide associatedwith the unreacted chromium carbide, about 11 volume percentchromium-tungsten carbide in WC/WC interstices, about 0.1 volume percentvoids, and about 85 volume percent unreacted WC. The composition rangeof the reaction product appears to be fairly narrow, based on EPAanalysis: about 75 weight percent Cr, about 12 weight percent W, andabout 12 weight percent C. Associated with the reaction product is about0.4 weight percent V, which is present in the WC starting powder at alevel of about 0.15 weight percent.

By observation using ATEM and use of the intercept method, average grainsize of the unreacted WC is about 0.2 microns. Average grain size of theunreacted Cr₃ C₂ is about 0.3-5 microns.

Physical properties of recovered parts are summarized in Table VIII. Thetest methods are described in Example 1.

                  TABLE VIII                                                      ______________________________________                                        Physical Properties and Wear Data of Example 23                               Property             Measured Value                                           ______________________________________                                        Density              14.3   g/cm.sup.3                                        Vickers Hardness, VHN                                                                              2428   kg/mm.sup.2                                       Palmqvist Toughness, W                                                                             21.2   kg/mm                                             Wear Number, WN      520    1/cm.sup.3                                        ______________________________________                                    

Due to the high hardness and wear resistance of this material, it can beexpected that it would perform well in applications similar to those forWC/Mo₂ C, with the potential added feature of improved oxidationresistance at higher temperature due to the presence of Cr₃ C₂.

Examples 24-26--Effect of Composition of Tungsten Carbide-ChromiumCarbide upon Resultant Physical Properties

The process of Example 23 is replicated except that the weight percentof Cr₃ C₂ in the powder mixture, and the preheat schedule, are changed.The preheat schedule used for the following parts involves a ramp fromroom temperature to 1500° C. at 10° C./min, followed by a 15 minute holdat temperature prior to pressure application. Three differentcompositions are used: 6, 10, and 20 weight percent Cr₃ C₂. Table IXsummarizes certain physical property test results for each composition.

                  TABLE IX                                                        ______________________________________                                        Physical Properties of Examples 24-26                                                              Vickers                                                                       Hardness, Palmqvist                                               Weight      VHN       Toughness                                      Example  % Cr.sub.3 C.sub.2                                                                        (kg/mm.sup.2)                                                                           W (kg/mm)                                      ______________________________________                                        24        6          2354      18.9                                           25       10          2500      21.4                                           26       20          2502      21.6                                           ______________________________________                                    

From this data, it appears that good material can be obtained from awide range of compositions. Examples 25 and 26 would in particular beexpected to demonstrate high wear resistance, by comparison with thehardness and wear data on Example 23, and by analogy from the AbrasionResistance vs. Hardness curve of FIG. 2. Similar results are expectedwith other compositions disclosed herein.

Example 27--Preparation of Densified Material using Titanium Carbide asthe source of AX, and Vanadium Carbide as the Source of B

The procedure of Example 23, save for a change in the preheat cycle, isrepeated using titanium carbide rather than tungsten carbide as a sourceof AX and vanadium carbide rather than Cr₃ C₂ as a source of B. Thestarting powder is a mixture of 88.4 weight percent titanium carbidehaving an average particle size of 3.8 microns and 11.6 weight percentvanadium carbide having an average particle size of 5.6 microns. Preheattemperature prior to pressure application changed to a cycle of 2 hoursat 600° C., 2 hours at 1400° C., and 2 hours at 1650° C.

Analysis of the microstructure by the techniques of Example 1 indicatesabout 91 volume percent mixed titanium-vanadium-tungsten carbide withsmall quantities of titanium carbide, 8.1 volume percent voids, and 1.0volume percent impurity carbide. No unreacted vanadium carbide isdetected using ASEM, EPA, ATEM, or XRD. EPA results indicate a fairlylimited composition range for the mixed carbide reaction product: about67 weight percent Ti, about 20 weight percent C, about 10 weight percentV, about 3 weight percent W, and about 0.2 weight percent Si. W isfound, by Proton-Induced X-ray Emission, in the powder mix at 3 weightpercent but not in the original powders prior to mixing. As such, thesource of W may be impurities in the attritor or the WC/Co attritormedia.

Physical properties of recovered parts are summarized in Table X. Thetest methods are described in Example 1.

                  TABLE X                                                         ______________________________________                                        Physical Properties of Example 27                                             Property             Measured Value                                           ______________________________________                                        Density              4.7    g/cm.sup.3                                        Hardness, VHN        1137   kg/mm.sup.2                                       Palmqvist Toughness, W                                                                             15.5   kg/mm                                             ______________________________________                                    

The hardness and wear resistance are expected to improve as the voidvolume decreases. Process optimization, perhaps through an increase inpreheat temperature, a reduction in starting powder grain size, or moreintense milling, is expected to provide a reduction in void volume.

Example 28--Preparation of Densified Material Using Tungsten Disilicideas the Source of AX and Molybdenum Disilicide as the Source of B

The procedure of Example 23 is repeated with a different mixture ofstarting powders and a preheat temperature of 1400° C. instead of 1500°C. The starting powders are 93.1 percent WSi₂ with an average particlesize of 6.1 microns and 6.9 percent MoSi₂ with an average particle sizeof 4.2 microns.

Analysis of recovered material reveals a microstructure containing about51 volume percent WSi₂, about 16 volume percent of a first reactionproduct with about 3 percent molybdenum, about 8 volume percent of asecond reaction product with about 56 percent molybdenum, about 18volume percent silica, about 6 volume percent WC with low Co, less thanone volume percent voids, and about one volume percent miscellaneousimpurities. Based upon EPA and ATEM, the first reaction product consistsof about 72 percent tungsten, 23 percent silicon and 3 percentmolybdenum. Unreacted molybdenum disilicide is not detected by ASEM, EPAor ATEM. The miscellaneous impurities and silica can be accounted for byconsidering impurity pickup from the attritor or attritor media, andreaction of the part with glass from the fluid die pocket in which it isheated and pressurized.

The recovered material has a density of 8.8 g/cm³ and a Vickers Hardnessof 1395 kg/mm². It is expected that physical properties of the materialcan be improved by reducing the amount of SiO₂ in the sample. Onepossible means of doing so is to process these materials in anoxygen-free environment. Other means are known to skilled artisans.

Example 29--Preparation of Densified Material using Titanium Nitride asthe Source of AX and Zirconium Nitride as the Source of B

The procedure of Example 23 is repeated, except for the preheatschedule, with a different mixture of starting powders. The powders are86.9 percent TiN with an average particle size of 1.6 microns and 13.1percent ZrN with an average particle size of 8.2 microns. The alternatepreheat schedule involves a 10 degree per minute ramp from roomtemperature to 1800° C., followed by a 15 minute hold at temperature.

Microstructure of the sample is analyzed by the methods of Example 1.There is an extensive reaction between the TiN and the ZrN, yielding atitaniumzirconium nitride which comprises about 85.6 volume percent ofthe sample. Unreacted TiN is present at about 2.0 volume percent, andthere is a trace amount of unreacted ZrN (<0.1 volume percent). Theremainder of the sample consists of about 4.7 volume percent ZrO₂, about1.0 volume percent tungsten silicide (with a low Fe content), and about6.6 volume percent voids. The tungsten silicide contaminant is presumedto come from the attritor/media. The composition of thetitanium-zirconium-nitride reaction phase is about 70.9 weight percenttitanium, about 6.9 weight percent zirconium, and about 22.2 weightpercent nitrogen.

Physical property measurements taken on recovered samples are listed inTable XI.

                  TABLE XI                                                        ______________________________________                                        Physical Properties of Example 29                                             Property            Measured Value                                            ______________________________________                                        Density             5.2    g/cm.sup.3                                         Hardness, VHN       1152   kg/mm.sup.2                                        Palmqvist           14.9   kg/mm                                              Toughness, W                                                                  ______________________________________                                    

The hardness of this material suggests what it should not have a levelof wear resistance as high as that of the material prepared inExample 1. This material is useful for applications where lower hardnessor wear resistance or both are acceptable.

Examples 30-32--Preparation of Densified Material using Hafnium Carbideas the Source of AX and Tungsten as the Source of B

The procedure of Example 23, save for a change in the preheat schedule,is replicated with different mixtures of starting powders. The startingpowders are hafnium carbide with an average particle size of 2.1microns, and tungsten metal with an average particle size of about onemicron. The ratio of HfC:W are either 85:15 or 70:30. The preheatschedule involves a ramp from room temperature at 10° C./minute to thedesired preheat temperature of 1650° C. or 1800° C. The samples are thenheld at temperature for fifteen minutes prior to pressure application.

Physical property measurements are presented in Table XII together withthe relevant preheat temperature and weight percent tungsten metalpowder.

                  TABLE XII                                                       ______________________________________                                        Physical Properties of Examples 30-32                                                       Pre-                                                                  Wt-%    heat            Hardness                                                                              Palmqvist                               Exam- Tung-   Temp.    Density                                                                              VHN     Toughness                               ple   sten    °C.                                                                             (g/cm.sup.3)                                                                         (kg/mm.sup.2)                                                                         (W) (kg/mm)                             ______________________________________                                        30    15      1650     12.5   1992    15.8                                    31    15      1800     11.9   1718    19.1                                    32    30      1650     12.6   2132    18.4                                    ______________________________________                                    

By observation of the samples under a scanning electron microscope, andthe use of an electron dispersive spectrometer, it appears that in allthree examples there is a reaction between the HfC and the W, as grainsof different proportions of Hf:W can be found.

Example 32 demonstrates an improvement in hardness and toughness overExample 30, with an increase in the percentage of tungsten metal.Example 31 shows no improvement in properties with an increase inpreheat temperature. The material of Example 32 shows promise forcutting tool and wear-resistant applications due to its high hardness.Similar results are expected with other compositions disclosed herein.

The materials of the present invention are, as noted hereinabove, usefulin a wide variety of end use applications where wear resistance orhardness or both are needed. The materials are particularly useful innozzles, such as sand blast nozzles and waterjet cutting nozzles, wearguides, bushings, powder compacting dies, valve parts, router bits,cutting tools, end mills, indexable inserts, wire drawing die parts andthe like.

What is claimed is:
 1. A material suitable for use in fabricatingarticles of manufacture requiring high degrees of hardness or wearresistance, the material consisting essentially of a substantially fullydense, complex, multi-phase, fine-grained product of an incompletereaction between AX and a source of B, the reaction taking place underpressure and at an elevated temperature, said product consistingessentially of at least one compound AX and at least one compound (A,B)Xwherein A and B are different materials selected from the groupconsisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum,chromium, molybdenum and tungsten and X is carbon.
 2. The material ofclaim 1 wherein A is selected from the group consisting of tungsten,hafnium or titanium and B is a material different from A selected fromthe group consisting of tungsten, zirconium, vanadium, chromium andmolybdenum.
 3. The material of claim 1 wherein A is tungsten and B ismolybdenum.
 4. The material of claim 1 further comprising a residualamount of the source of B.
 5. The material of claim 3 wherein the sourceof B is molybdenum subcarbide (Mo₂ C).
 6. The material of claim 1wherein (A,B)X is tungsten/molybdenum carbide product of varyingstoichiometry, the product having an average composition comprising fromabout 60 to about 99 percent by weight tungsten, from about one to about40 percent by weight molybdenum and from about four to about ninepercent by weight carbon.
 7. The material of claim 6 wherein (A,B)X hasan average composition which comprises from about 77 to about 89 percentby weight tungsten, from about 5 to about 16 percent by weightmolybdenum and from about 5 to about 8 percent by weight carbon.
 8. Thematerial of claim 3 having a Vickers hardness of at least about 2200kg/mm² measured using a 1 kg load, and having an abrasion wearresistance of at least about 500 cm⁻³ measured by the ASTM G65 method.9. The material of claim 8 wherein the Vickers hardness is at leastabout 2400 kg/mm² measured using a 1 kg load.
 10. The material of claim1 having a density of more than about ninety percent of theoreticaldensity.
 11. The material of claim 2 having a grain size of less thanabout five microns.
 12. The material of claim 11 wherein A is tungstenand B is chromium.
 13. The material of claim 12 wherein the source of Bis chromium carbide.